this invention relates to the field of intravascular catheters, and more particularly to a catheter with a lubricious catheter shaft and a method of manufacture thereof. In percutaneous transluminal coronary angioplasty (PTCA) a balloon catheter is used to restore free flow in a clogged coronary vessel. The catheter is maneuvered through the patient""s tortuous anatomy and into the patients coronary anatomy until the balloon is properly positioned across the stenosis to be dilated. Once properly positioned, the balloon is inflated with liquid one or more times to a predetermined size at relatively high pressures (e.g. greater than 4 atm) to reopen the coronary passageway. After the balloon is finally deflated, blood flow resumes through the dilated artery and the balloon catheter can be removed therefrom.
Balloon catheters generally comprise an elongated shaft with an inflatable balloon on the distal end of the shaft. An inflation lumen extending within the shaft is used to deliver inflation fluid to the balloon interior. In over the wire or rapid exchange designs, a guidewire is slidably received within a guidewire lumen extending at least within a distal section of the catheter.
A lubricious coating is typically provided on the outer surface of the catheter shaft to facilitate the movement of the catheter within the patient""s body lumen. Additionally, a lubricious coating may be provided on an inner surface of the shaft which defines the guidewire lumen, to facilitate the movement of a guidewire therein. The lubricious coatings generally comprise silicone, polymeric materials, or hydrophilic compounds which become lubricious after absorbing water. However, a lubricious coating with high lubricity may often have poor adhesion to the catheter shaft surface. In addition to coatings which provide lubricity, catheter shafts may be formed from a hydrophilic polymeric blend. However, one challenge has been providing high lubricity without a loss of other catheter shaft characteristics such as low profile, strength, flexibility, and case of manufacture.
Therefore, what has been needed is a balloon catheter having a lubricious shaft with improved shaft performance characteristics, which retains it""s lubricity after repeated use, and which provides improved ease of manufacture. The present invention satisfies these and other needs.
The invention is directed to an intravascular catheter which has a lubricious catheter shaft formed from a polymeric blend comprising a thermoplastic polymeric component and a lubricious polymeric component. The lubricious component is immiscible in the thermoplastic component and exists as elongated fibers having a high aspect ratio. In accordance with the invention, the lubricious component exists as a separate phase of elongated fibers which provide improved lubricity to an extruded catheter shaft formed of the polymeric blend of the invention. The aspect ratio of the hydrophilic component fibers is about 10 to about 100, and preferably about 20 to about 50, and most preferably at least about 20. The high aspect ratio of the lubricious component fibers increase the surface area of the lubricious component on the surface of the catheter shall, and consequently increase the lubricity of the catheter shaft. Additionally, the lubricious component fibers are longitudinally oriented, which further enhances the effect of the lubricious component on the lubricity of the shaft.
The polymeric blend of the invention preferably comprises a minor amount of the lubricious component and a major amount of the thermoplastic component, Because the elongated fibers of the lubricious component provide improve lubricity, a minor amount of lubricious component nonetheless provides substantial lubricity to the catheter shaft formed thereby. In a presently preferred embodiment, the lubricious component comprises about 5 to about 20 percent by weight of the polymeric blend, and most preferably less than about 10 percent by weight of the blend. The weight percent of lubricious component must be sufficiently low that the immiscible lubricious component readily mixes into the matrix polymeric component.
In a presently preferred embodiment, the intravascular catheter of the invention is a balloon catheter generally comprising an elongated catheter shaft with an inflatable member on a distal portion of the chanter. The catheter shaft has an outer tubular member and an inner tubular member disposed within the outer tubular member inner lumen, with a distal extremity of tile inflatable member sealed about and secured to a distal extremity of the inner tubular member. A proximal extremity of the inflatable member is sealed about and secured to a distal extremity of the outer tubular member or the two are formed as an integral member. In a presently preferred embodiment, the lubricious catheter shaft of the invention forms the inner tubular member of a balloon catheter, so that guidewire movement therein is facilitated by the lubricity of the inner tubular member. However, the lubricious catheter shaft may form an outer member of the catheter, and thereby facilitate movement of the catheter within a body lumen of the patient.
A method of forming a lubricious catheter shaft of the invention comprises extruding the thermoplastic polymeric component and the immiscible lubricious component blend to form tubing. The tubing is stretched in a cold state (i.e. room temperature) so that the lubricious component exists as elongated fibers having a high aspect ratio,